In integrated circuits, it may be desirable, after the circuit is manufactured, to permanently store information within it, or to form or alter its connections. Fuses or other devices may be used for this purpose. In some cases, a laser is used to open a link in the circuitry of a semiconductor device. However, the use of lasers in such circumstances requires precise, time-consuming alignment of the laser to avoid damaging neighboring circuitry and devices.
Electromigration fuses (eFuses) provide a more recent, less destructive alternative to the use of lasers. In general terms, an eFuse comprises a cathode and an anode connected by a fuse link. The fuse link is comprised of a conductive material, such as a metal or metal silicide, e.g., titanium, tungsten, aluminum, copper, titanium silicide, nickel silicide, etc. A current is applied across the fuse link such that its conductive material electromigrates from one portion of the fuse link to another. The result is a great reduction in the conductivity of the eFuse and a correspondingly great increase in its resistance. Thus, the fuse is “blown” and the circuitry of the semiconductor device is altered or “programmed” (e.g., by disabling circuitry connected to the eFuse, invoking redundant or alternate circuitry of the device, permanently storing information in the eFuse, etc.). While eFuses enable less destructive alteration of a device's circuitry, programming an eFuse requires physical connection to the circuit to provide the necessary power, which is time-consuming, expensive, and limiting of the locations and circumstances in which such programming may be done.